Helena Bonham Carter has decidedly mixed feelings about playing an ape in Planet Of The Apes.

On the one hand, it's a plum role in what looks like being one of the must-see movies of the summer.

On the other, she's not going to get recognised by a fair number of the cinema-going public, or at least she shouldn't, beneath all that ape gear.

And that means that she's likely to retain her demure, only-ever-seen-in-a-period-drama reputation, one that drives her up the wall.

Why does she have such an image? It's true that she's appeared in period dramas - notably A Room With A View - but she's done plenty more besides.

"It just seems that, once you're stuck in the public's mind as being an actress that plays a particular type of role, it's very hard to shift that perception," she says.

"And the media doesn't help. I've seen film reviews of period dramas where the reviewer has said the Helena Bonham Carter role was played by so-and-so. It really is ingrained."

Helena's efforts to alter her soft, sweet-as-pie image have included the role of a swearing, vodka drinking, sexually liberated woman in a yet-to-be-seen British film called Talking Dirty.

And she's quick to talk up the differences between her and her genteel image.

"I smoke, I drink alcohol and I consume far too much coffee. I swear, I belch and I'm a lot more muscular than people think I am," she stresses.

All that said, she's probably landed the part which equates most closely to that of the sensitive female in Planet Of The Apes, a remake of the 1968 picture of the same name.

She plays Ari, a chimpanzee who campaigns for human rights. Ari lives on a planet where the monkey is king but she doesn't believe that humans, the hairless ones, as they're called, should be enslaved.

She is firmly of the opinion that Leo Davidson (Mark Wahlberg), whose ship crash-landed on the ape planet and who was subsequently imprisoned, can prove to the world that humans and apes should be treated equally.

In preparing for the film, Helena, 35, had to attend an ape school where she learned to mimic the creatures' movements.

And she underwent four hours of make-up a day in order to look like Ari.

The actress reckons that strapping on a corset, which of course, she's occasionally had to do during the run of her career, was relatively painless, compared to the rigours of turning her into an ape.

"The process began with being fitted with a bald cap and protruding teeth and then rubber ears," she says.

"Then a mask was glued to my face, followed by facial hair and a wig.

"I was getting up at two in the morning so we could begin shooting at seven. Those early-morning hours in make-up were absolutely essential, though. I certainly wasn't going to keep the make-up on overnight.

"Can you imagine going into a restaurant dressed as an ape? I would have been offered nuts and banana sandwiches!

"But obviously I kept the make-up at all times during the day and the effect that had on some of my friends was amazing.

"They'd visit me on the set and although they'd know it was me beneath the outfit, they'd not look at me while they were talking to me.

"It was as if they were embarrassed or spooked by me looking so very different."

The effect of all that early morning preparation is to make Helena appear as cute as it's possible for an ape to be.

The cuteness, and sex appeal, of her character is a bit of a sore point, as far as Helena is concerned.

Producer Tim Burton has been quoted as saying that he wanted Helena's character to be "sexually attractive to men".

Indeed, in the original script there was a sex scene between Ari and Leo although it was dropped by the time filming started.

And for that, Helena is enormously grateful.

"I think there was a very real danger that that particular scene wouldn't have looked right," she says.

"That's not to say the relationship between our characters isn't an emotional one, one that's conveyed in many different ways.

"But I firmly believe that any kind of kissing or sex between us would have not only looked ridiculous but may even have been seen as kinky or perverse.

"I mean come on, an ape kissing a human passionately? I think a lot of people would have been disgusted by that and it would have been a talking point that overshadowed the rest of the film."